Abstract
In this study, a trans-cavitating propeller is defined as a propeller whose design condition is between those of conventional propellers and supercavitating propellers. A propeller for high speed vessel of about 30 knots falls in such a design condition, where a suitable propeller design method has not yet been found. For such a condition, it would be realistic to adopt supercavitating blade sections near the tip and noncavitating ones near the root, since ordinary blade sections can lead to harmful violent cloud cavitation. This study investigates foil sections suitable for a trans-cavitating propeller. The purposes of this study are to investigate the noncavitating and supercavitating foil design methods for such intermediate design condition, and to find a criterion to switch the design between noncavitating and supercavitating foils.By prescribing pressure distributions, one noncavitating foil section and one supercavitating foil section are designed for a condition of r/R =0.7 position of a trans-cavitating propeller. Cavitation performance as well as noncavitating performance are examined by the noncavitating and cavitating foil theories, and by the cavitation tunnel tests such as hydrodynamic force measurement and cavitation observation. From these test results, the foil performance and design method are evaluated as well as the accuracy of the theoretical prediction are discussed. The following results are obtained.(1) The noncavitating foil section did not cavitate at the design condition as expected. High lift/drag ratio of 35.3 was obtained. Wide cavitation bucket of about 2 deg. was also achieved. Theoretical prediction gave slightly higher lift coefficient by 0.25 deg. in the angle of attack and narrower cavitation bucket than the experiment. The theory should be further improved in these points.(2) The supercavitating foil section generated supercavitation at the design point as expected. High lift/drag ratio of 33.1 was obtained. The predictions by a linear supercavitating foil theory showed fine agreement with the experimental results.
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